1. Field of the Invention
The present invention relates to an effect pigment comprising a plate-shaped non-metallic substrate and a copper-containing coating, to a method for the production thereof and to the use of this effect pigment in anti-fouling coatings. The invention furthermore relates to anti-fouling coatings comprising such an effect pigment.
2. Description of Related Art
Underwater coatings consist predominantly of a waterproof coating (corrosion protection, osmosis protection, protection against mechanical damage) and a fouling-inhibiting coating as paint finish. This fouling-inhibiting coating, by continuous washing out of biocides, is to prevent fouling organisms such as algae, fungi, snails, mussels and further microorganisms, the so-called fouling, from attaching themselves to a ship's hull for example. Fouling organisms increase the frictional resistance and the weight of a ship. They thus contribute to an increased fuel consumption and thereby to increased operating costs. The biocides only act when they are released from the paint into the seawater (“leaching”). If this is not the case, they are not absorbed by the organisms and cannot deploy their biocidal effect. The integration of the biocides in the paint thus must represent a compromise between a washout of the biocides that is too fast and a discharge into the seawater that is too slight. In other words, the cost-intensive renewal of the paint is to be minimized and at the same time the protection against fouling is to be maintained. Some of the biocide-containing anti-fouling systems predominantly used until now have, in the past, caused damage worldwide in the marine environment, with the result that particular biocides, such as e.g. dichlorodiphenyltrichloroethane (DDT), organotin, arsenic and mercury compounds, have been banned internationally. As a response to the environmental problem of biocide-containing anti-fouling systems, biocide-free non-stick coatings, predominantly based on silicone, were brought onto the market. As an example so-called sharkskin is to be named here, which consists of nanostructured silicone with irregular, but regularly repeating topography. The beneficial claim of products based on sharkskin, however, is only conditionally correct, as sharkskin is covered with special scales which clean each other by the constant movements of the sharks and fouling is not repelled just by the roughness. An ideal surface structure which similarly prevents all fouling organisms from settling has thus far not yet been able to be identified (B. T. Watermann, D. Daehne, C. Fürle, Einsatz von Nanomaterialien als Alternative zu biozidhaltigen Antifouling-Anstrichen and deren Umweltauswirkungen, Umweltbundesamt Texte 40/2010, UBA-FB No.: 001301, funding reference number: 363 01 174, pp. 14, 19, 23, 24 (hereafter called “Umweltbundesamt”); R. Kätscher, J. Ranke, M. Bergenthal, J. Warrelmann, Vorstudie zum Bewuchsschutz für Seeschiffe, January 1999, 2nd part p. 5, (hereafter called “Vorstudie”)).
Anti-microbial compositions and polymers containing these anti-microbial compositions are known from EP 0 677 989 B1. The anti-microbial compositions comprise inorganic particles which have a primary surface coating made of a metal or a metal compound with anti-microbial properties and are covered with a secondary protective layer. This primary coating has a proportion by weight of from 0.05 to 20 wt.-% relative to the substrate. The secondary protective layer is to influence the release of the anti-microbial component into the surrounding polymer matrix.
Anti-bacterial or electrically conductive compositions containing inorganic particles coated with metals are described in EP 0 427 858 A1. If the particles are to have an anti-bacterial effect, the proportion of the coating is 0.1 to 20 wt.-%, relative to the total weight of the particles. If the particles are to be electrically conductive, the proportion of the coating is at least 25 wt.-%, relative to the inorganic particles. The average size of the particles is between 0.1 and 5 μm. With such small particle sizes, only an insufficient barrier effect is guaranteed. Furthermore, the specific surface area, i.e. the surface area per unit of weight, of these particles is disadvantageously very large, with the result that a high release rate of the anti-bacterial component is brought about.
Anti-microbial pigments comprising a mixture of inorganic pigment and silver oxide as anti-microbial component are known from WO 2004/092283 A2. The silver oxide can be replaced by other anti-microbial compounds. The anti-microbial compound content lies in a range of from 0.001 to 10 wt.-%, preferably from 0.005 to 5 wt.-%, in each case relative to the inorganic pigment. The inorganic pigment can have any desired shape.
The use of copper platelets coated with silicon dioxide in anti-fouling coatings which are commercially available as Resist AT, LT or CT (from Eckart) is known from U.S. Pat. No. 7,147,921 B2.
Copper-containing anti-fouling coatings in which the amount of copper has been reduced by addition of graphite are known from US 2004/0197322 A1.
A predominantly spherical powder which has been covered with copper(I) oxide by means of electrolysis is described in EP 2 246 395 A1. The copper(I) oxide particles are adhesively fixed to the surface. The proportion of water-soluble chloride ions is less than 0.1 wt.-% relative to the total weight of the powder. The powders are to be able to be incorporated well into anti-fouling coatings and at the same time increase their storage stability.
WO 2011/010663 A1 describes particles that are covered with copper(I) oxide by means of electrolysis and which can be used to increase the storage stability in anti-fouling coatings. The copper(I) oxide covering here consists of an accumulation of octahedral copper(I) oxide particles.
Composite pigments for anti-fouling coatings in which copper(I) oxide particles are electrolytically deposited on the surface of SiO2 and/or Al2O3 powder are described in JP 01213368 A.
According to FR 2 937 043 A1 pearlescent pigments are used in anti-fouling coatings to attract fish. The organisms settling on a ship's hull are to serve as food for the fish.
At the same time, the pearlescent pigments are to give the anti-fouling coating a visually attractive appearance.
Biocidal compositions comprising an inorganic silver, copper or zinc compound as well as a polymeric carrier are known from WO 2010/125323 A1. The copper compound can be selected for example from basic copper chloride, basic copper sulfate, basic copper carbonate, copper oxide or copper hydroxide. Disadvantageously, coated organic carrier materials are as a rule only conditionally temperature-stable. When used in solvent-containing systems, undesired phenomena such as swelling or even complete disintegration of the carrier material can also occur.
Anti-fouling coatings are known from JP 54047730 A which comprise for example basic copper chloride and red phosphorus, which is responsible for the controlled washout of copper ions.